Victim: James Barker, 12, was among the 29 people killed in the 1998 who Omagh bombing

A father whose young son was murdered in the Omagh atrocity will today launch a one-man protest against former IRA commander Martin McGuinness’s presence at a state banquet with the Queen.

Victor Barker’s 12-year-old son James was among 29 people who were killed in the 1998 bombing.

The Surrey solicitor will stand outside the main gate at Windsor Castle waving a placard which reads, ‘A terrorist in white tie and tails is still a terrorist. Martin McGuinness – it’s time to tell the truth’.

Mr Barker said: ‘I was born in Windsor and I thought I’ve got to do something. People need to be reminded of his credentials.

‘There is no place for a terrorist at the Queen’s table.’

Referring to the Real IRA attack on Omagh, Mr Barker added: ‘[McGuinness] knows of things and of people who could give evidence and he will not do so because it breaches their code of omerta. I have nothing against the Irish people. My beef is with the IRA.’

Mr McGuinness, the Northern Ireland Deputy First Minister and Sinn Fein politician, will be among the guests at the state banquet at Windsor Castle. He will also attend other events to mark this week’s official visit to the UK by Irish president Michael Higgins.

Mr Barker played a leading role in launching the Omagh families’ campaign, backed by the Daily Mail, to help raise money to bring the terrorists behind the attack to justice.

While no one has been convicted over the atrocity in criminal courts, in 2009 four republicans were found liable in the landmark civil case taken by some of the bereaved families and ordered to pay £1.6million compensation.

Ambitions: James, a sports fan, had been excited about going to a Belfast prep school on the path to fulfilling his ambition to follow in his father's footsteps and become a lawyer

The Barker family had moved their four children to County Donegal from England a year before the bombing to ‘give them a better quality of life’.

Demonstration: Surrey solicitor Victor Barker will stand outside the main gates of Windsor Castle with a placard while Martin McGuinness attends a banquet

James, a sports fan, had been excited about going to a Belfast prep school on the path to fulfilling his ambition to follow in his father’s footsteps and become a lawyer.

Wearing a Three Lions football shirt, he was on a coach trip which had visited a theme park before stopping off in the town on a whim to do some shopping.

Mr Barker has repeatedly challenged Mr McGuinness and Sinn Fein leader Gerry Adams to call for witnesses to come forward and help identify the people involved in placing the 500lb car bomb in the middle of Omagh on a busy Saturday shopping day.

He said: ‘There is no realistic possibility of a criminal conviction unless someone comes forward. Either they, or people they know, can identify the people involved in Omagh.’

Former MP Mr McGuinness, who refused to take his Commons seat because of the oath of allegiance to the Monarch, snubbed a gala banquet in honour of the Queen during her visit to Ireland in 2011.

The idea of an IRA leader dining with the Queen would have been unthinkable a few years ago. But in 2012 – more than 30 years after the Queen’s cousin, Lord Mountbatten, was murdered by the IRA – she agreed to meet Mr McGuinness for the first time and shake hands with him in public during a visit to Belfast.